Herbicide-resistant Palmer amaranth continues to invade many areas of Michigan and the Upper Midwest. Our first encounter with Palmer amaranth in Michigan occurred in the fall of 2010.

A soybean producer in southwest Michigan was struggling with management of a weed he did not recognize. We were able to identify this weed as Palmer amaranth, and through greenhouse testing confirmed high levels of resistance to both glyphosate (Roundup) and ALS-inhibiting herbicides.

At this time, we also noticed several neighboring alfalfa fields where Palmer amaranth seed heads were poking just above the alfalfa canopy....